什么是std :: vector :: _ emplace_back_slow_path / std :: vector :: _ push_back_slow_path？

Question

When using a call profiler, I noticed a high runtime cost and a high number of allocations in std::vector::_emplace_back_slow_path . Because I am concerned about performance, I want this to say "fast path". What am I doing wrong?

Answer 1

Looking at the implementation , the "slow path" is the path taken if a reallocation is needed:

vector<_Tp, _Allocator>::emplace_back(_Args&&... __args)
{
    if (this->__end_ < this->__end_cap())
    {
        // This is the code that you could call the "fast path"
    }
    else
        __emplace_back_slow_path(_VSTD::forward<_Args>(__args)...);
}

This also applies to std::vector::_push_back_slow_path .